Rangefinder for measuring the distance of an object having a luminous spot

ABSTRACT

A rangefinder for measuring the distance of an object having a luminous spot has a convergent optical receiving system for picking up rays from the spot and converging them on to a sensing device. This device has a mirror wherein the edges of the reflective surface thereof comprises a separator element including a peripheral separating line sensitive to the convergence of the rays, and is arranged substantially on the caustic of the optical receiving system at a point remote from the optical axis of the system. The system may be at least one annular portion of a convergent system devoid of its central part. The caustic may have a cusp for greater concentration of light on said edges of the reflective surface of the mirror. The converging system may be formed by at least a part of a ring of a convergent system of lenses or of a concave Mangin mirror. The light projection device may be located on the axis of the optical system and in front of the photosensitive device, in the case where the central part of the optical system is not used.

lite Sttes atet Lietar [is] 3,652,159 [451 Mar. 28, 1972 [54]RANGEIFINDER FOR MEASURING THE DISTANCE OF AN OBJECT HAVING A LUMHNOUSSPOT [72] Inventor: Christian Lietar, Yverdon Vaud, Switzerland [73]Assignee: Paillard S.A., Sainte-Croix, Vaud, Switzerland [22] Filed:Sept. 15, 1969 [211 App]. No.: 857,813

[30] Foreign Application Priority Data Sept. 27, 1968 Switzerland..l4586/68 [52] U.S. Cl. ..356/4, 250/204 ..G0lc 3/08 Field oiSearch..356/4, 5, 109, HO; 250/204 [5 6] Reierences Cited FOREIGN PATENTS ORAPPLICATIONS 449,985 4/1968 Switzerland ..356/4 551,427 3/1957 Belgium..356/4 Primary Examiner-Richard A. Farley Assistant Examiner-S. C.Buczinski Attorney-Emory L. Groff and Emory L. Groff, Jr.

[ S 7] ABSTRACT A rangefinder for measuring the distance of an objecthaving a luminous spot has a convergent optical receiving system forpicking up rays from the spot and converging them on to a sensingdevice. This device has a mirror wherein the edges of the reflectivesurface thereof comprises a separator element including a peripheralseparating line sensitive to the conver- ,7

gence of the rays, and is arranged substantially on the caustic of theoptical receiving system at a point remote from the optical axis of thesystem. The system may be at least one annular portion of a convergentsystem devoid of its central part. The caustic may have a cusp forgreater concentration of light on said edges of the reflective surfaceof the mirror. The converging system may be formed by at least a part ofa ring of a convergent system of lenses or of a concave Mangin mirror.The light projection device may be located on the axis of the opticalsystem and in front of the photosensitive device, in the case where thecentral part of the optical system is not used.

8 Claims, 1 Drawing Figure PATENTEUHMZ28 IQTE 3,652,159

INVENTOR C/lle/s mm A /E TAR ATTORNEY RANGEFTNDER FOR MEASURING THEDISTANCE OF AN OMIEUJI HAVING A LIUMINQUS SPOT The present inventionrelates to a rangefinder for measuring the distance of an object havinga luminous spot.

There are already known rangefinders for measuring the distance of anobject having a luminous spot, comprising a receiving convergent opticalsystem, intended to pick up rays from the spot and to make them convergeon the line of separation of a device sensitive to the distance ofconvergence of the said rays.

Such a convergent optical system is illustrated and described in U.S.Pat. No. 3,558,894, assigned to the same assignee as the presentapplication which is an improvement over the device of said patent. Ingeneral, the luminous spot is obtained by means of a projector directinga luminous beam on to the object whose distance it is desired tomeasure. By luminous beam," there is understood any beam having thegeneral characteristics of light, this term covering particularly thecase of rays whose wavelength is outside the visible spectrum, that isto say ultraviolet or infrared rays.

In rangeflnders of this type, the receiving optical system and thedevice sensitive to the distance of convergence of the rays presentconstructional problem relatively difficult to resolve.

In fact, good functioning of this type of range-finder requires luminousrays issuing from a point-object situated on the axis of the said systemnot converging on this axis, but on a separating line provided by theedges of the light sensitive device which must generally be spaced fromthe axis, this separating line being able to be continuous,discontinuous or even constituted by two distinct lines symmetrical withrespect to the axis.

To realize this condition, the first solution which appears, is to use areceiving optical system, comprising one or several toroidal surfaceswhich then give, from a point-object situated on the axis, an image inthe form of a circular line. But these toroidal surfaces are difflcultto produce and consequently are of high cost.

lt is an object of the present invention to provide a rangefinder inwhich toroidal surfaces are replaced by simple spherical surfaces whichare easier to manufacture with precision and are less expensive.

Other objects and advantages will emerge from the description whichfollows.

According to the invention, there is provided a rangefinder, in whichthe edges of the reflective surface of a mirror of the sensitive deviceare arranged appreciably on the caustic of the receiving optical system,at a point remote from the optical axis of the said system.

In order that the invention may be more fully understood, an embodimentof a rangefinder according to the invention is described below purely byway of illustrative but non-limiting example, with reference to theaccompanying schematic drawing.

Referring now to the drawing, a rangeflnder comprises a convergentreceiving optical system which is formed by a Mangin mirror 1. As isknown, mirrors of this type are concave and have a spherical frontsurface 2 and a rear surface 3 similarly s herical. The rear surfacealong is reflecting, so that rays 4 reaching the mirror must pass twicethrough the thickness of the glass before being reflected towards thefocus of the mirror. By suitable choice of the radii of curvature of thefront and rear surfaces of the mirror, of the refractive index of theglass and of the thickness of the mirror, it is generally sought tocorrect the mirror so that the marginal rays are reflected with accuracyon to the focus of the mirror.

On the other hand, in the mirror shown, the parameters of the mirror areselected so as to obtain a caustic 5 having a cusp ti at a pointrelatively distant from the optical axis 7 of the mirror. As is known,the caustic is an envelope-surface of rays reflected by the mirror.

The central part of the mirror I is covered by an opaque non-reflectinglayer 8. Moreover, this mirror comprises a diametrical band, so that itonly presents finally two reflecting portions 9, 10 diametricallyopposite and arranged on both sides of the opaque layer 8.

The rays substantially parallel to the optical axis 7 striking theportion 9, and which are included between the extreme rays 4 and 4,shown in the drawing, are reflected as indicated at 11 and 11, andintersect in proximity to the cusp 6 of the caustic 5.

It is thus possible to locate the edge 12 of a separate elementcomprising a reflecting layer 15 deposited on a circular glass 14 at aspot where the luminous intensity is relatively high and where thecutoff point of the reflected rays II and Ill is substantially displacedas a function of the incidence of the rays 4 and 4' on the mirror. Thelight is thus, according to the distance of the object, received by thephotosensitive element 17 or, after reflection on the reflecting layer15, on the other photosensitive element 16. Thus it will be seen thatthe edges of the separator element or reflecting layer 15 split the luminous flux forming the cusp into two separate beams with the proportionof the luminous fluxes forming these beams being dependent upon theaxial location of the separator element. Moreover, as the receivingoptical system comprises two portions 9, 10 of the mirror, the edges 12and 13 of reflecting surface 15 can be placed on the path of thereflected rays for each of the portions 9 and 10 of the mirror.

At the lower part of the drawing, there are shown extreme rays 4" and4", arising from a point-object situated on the optical axis 7 close tothe mirror 1. In this case the rays concerned are not parallel to theoptical axis and after reflection define a caustic curve 5', having acusp 6, which is in a different position along the axis from thatpresented by the rays 4 and 4 parallel to the optical axis.

In a specific example of the receiving optical system, the Mangin mirrorhas been produced from a glass having an index of refraction of 1.51 anda constringence or Abbe number of 64. The radius of curvature of thefront surface is 89.6 mm. and that of the rear surface 118.2 mm. Themaximum outer diameter is 112 mm., whilst that of the opaque layer 8 is74 mm. The cut-off point of the reflected rays, in the case of rays 4and 4' parallel to the optical axis, is then situated at 58.8 mm. fromthe bottom of the mirror and at 2.5 mm. outside the optical axis.

In general, rangefinders comprising a receiving optical system to pickup rays from a luminous spot are also provided with a projector,directing a beam on to the object whose distance it is desired tomeasure, to form thereon the said luminous spot. In the case illustratedin the drawing, as the central part of the mirror 1 is not used, it ispossible to place the light source L and its reflector R on the opticalaxis 7 in from of the photosensitive element 17.

It is well understood that there can be provided numerous variations ofthe embodiment shown and that in particular the optical system couldhave more than two parts of a ring of a concave mirror, or even beformed by a complete ring. In this latter case, the image of apoint-object would no longer be given in the form of two portions ofarcuate lines, as in the case shown in the drawing, but in the form of acomplete circular line.

Neither is it indispensable that the convergent system be constituted bya concave mirror, since it could very well be produced from receivingdevices having similar operating conditions, these receiving devicesincluding an annular part of a convergent system comprising one orseveral lenses, or again several portions of such an annular part.Neither is it necessary that the caustic of the receiving system have acusp, but this feature is however advantageous, since it enables theobtaining of a greater concentration of light on the separating lines 12and 13.

All such and other changes and modifications may be made in theembodiments described above, without departing from the essentialconcept of the invention as defined in scope by the appended claims.

I claim:

1. In a rangefinder for measuring the distance of an object having aluminous spot and wherein a convergent optical receiving system isadapted to pick up rays from said spot and to make them converge on anedge of a sensing device sensitive to the distance of convergence of thesaid rays, the improvement, wherein said convergent optical receivingsystem includes a portion of a Mangin mirror corresponding to a zone ofsaid mirror for which the caustic forms a cusp, said sensing deviceincluding a separator element movable along the optical axis of saidconvergent optical receiving system to remain substantially adjacent thearea generated by said cusp of said caustic when the distance of theobject to be measured is varied within the useful range of the rangefinder, said separator element separating the luminous flux forming thecusp portion of said caustic into two separate beams with the proportionof the luminous fluxes forming the two beams being dependent on theposition of said separator element with respect to that of the cuspportion of said caustic and said sensing device including photoelectricmeans adapted to detect the intensity of the luminous fluxes of the twobeams separated by said separator element.

2. A rangefinder according to claim 1, wherein the convergent opticalsystem is constituted by at least one annular portion of a convergentsystem devoid of its central part.

3. A rangefinder according to claim 2, including a light projectiondevice located on the axis of the optical system and in front of thesensing device.

4. A rangefinder according to claim 1, wherein the convergent opticalsystem is formed by at least a part of a ring of a convergent system oflenses.

5. A rangefinder according to claim ll, wherein the convergent opticalsystem is formed by two diametrically opposite portions of a Manginmirror.

6. A rangefinder according to claim 1, wherein the convergent opticalsystem is formed by a ring of a convergent system of lenses.

7. A rangefinder according to claim 1, wherein the convergent opticalsystem is formed by a ring of a concave Mangin mirror.

8. A rangefinder according to claim 1, wherein the Mangin mirror isproduced of a glass having a refractive index of about 1.51 and an Abbenumber of about 64.

1. In a rangefinder for measuring the distance of an object having aluminous spot and wherein a convergent optical receiving system isadapted to pick up rays from said spot and to make them converge on anedge of a sensing device sensitive to the distance of convergence of thesaid rays, the improvement, wherein said convergent optical receivingsystem includes a portion of a Mangin mirror corresponding to a zone ofsaid mirror for which the caustic forms a cusp, said sensing deviceincluding a separator element movable along the optical axis of saidconvergent optical receiving system to remain substantially adjacent thearea generated by said cusp of said caustic when the distance of theobject to be measured is varied within the useful range of the rangefinder, said separator element separating the luminous flux forming thecusp portion of said caustic into two separate beams with the proportionof the luminous fluxes forming the two beams being dependent on theposition of said separator element with respect to that of the cuspportion of said caustic and said sensing device including photoelectricmeans adapted to detect the intensity of the luminous fluxes of the twobeams separated by said separator element.
 2. A rangefinder according toclaim 1, wherein the convergent optical system is constituted by atleast one annular portion of a convergent system devoid of its centralpart.
 3. A rangefinder according to claim 2, including a lightprojection device located on the axis of the optical system and in frontof the sensing device.
 4. A rangefinder according to claim 1, whereinthe convergent optical system is formed by at least a part of a ring ofa convergent system of lenses.
 5. A rangefinder according to claim 1,wherein the convergent optical system is formed by two diametricallyopposite portions of a Mangin mirror.
 6. A rangefinder according toclaim 1, wherein the convergent optical system is formed by a ring of aconvergent system of lenses.
 7. A rangefinder according to claim 1,wherein the convergent optical system is formed by a ring of a concaveMangin mirror.
 8. A rangefinder according to claim 1, wherein the Manginmirror is produced of a glass having a refractive index of about 1.51and an Abbe number of about 64.